1. Field of the Invention
The present invention relates to switching power supplies, and more particularly to control systems used to control the switching cells that form part of the structure of such power supplies.
2. Description of Related Art
Switching power supplies are the step-down or step-up transformer converters of DC-DC power. In the particular case of the step-down transformers, such power supplies conventionally include an inductor positioned, for example, on the output side of the converter. This inductor is connected by a first changeover switch to a DC-DC power supply, and to ground by a second changeover switch.
FIG. 1 illustrates the general structure of a conventional step-down transformer DC converter that is used to supply power to a load R. FIG. 2 shows timing charts indicating the evolution of the current circulating in the inductor and the variation of the control signals of the first and second changeover switches P and N, respectively. In switching power supplies of this type, the control circuit controls the first and second changeover switches so as to switch them in a way that prevents the current circulating through the inductor from becoming negative.
Normally, the control of the changeover switches is carried out on the basis of a measurement of the current circulating through the inductor that is made by using the appropriate current detectors. However, this causes significant inconveniences in terms of the power used and yield, especially for light loads.